Power storage devices such as batteries each include a structure body including a positive electrode and a negative electrode disposed via a separator. A defect in the structure body leads to a defect in the power storage device, and thus, in production of power storage devices, it is necessary to detect a structure body in which an abnormal event such as a short or an open occurs between the positive electrode and the negative electrode.
In general, detection of an abnormal event occurring in a structure body is performed by measuring an insulation resistance using, e.g., a megohmmeter. Where a megohmmeter is used, acceptability determination is made based on a resistance value in a limited period of time immediately before a current value after application of an inspection voltage converges. More specifically, a direct-current voltage is applied to the structure body, a value of the applied voltage and a value of flowing current after a certain period of time are measured, and a resistance value is calculated from the measured applied voltage value and current value. Since such resistance value after a certain period of time calculated as above is used for acceptability determination, and where a megohmmeter is used, it is difficult to fully detect an abnormal event during the inspection of the structure body.
A method in which, while an inspection voltage is applied to a precursor of a secondary battery such as a structure body, a current flowing as a result of the inspection voltage application is measured at a predetermined time interval to detect an abnormal event between a positive electrode and a negative electrode has been provided (for example, Patent Literature 1). In this method, a result of the measurement is compared with an acceptable range based on a preset reference value, and if the result has a value failing beyond the acceptable range, the precursor is determined as a defective product.